Generally, in case of an audio signal, an audio signal encoding apparatus compresses the audio signal into a mono or stereo type downmix signal instead of compressing each multi-channel audio signal. The audio signal encoding apparatus transfers the compressed downmix signal to a decoding apparatus together with a spatial information signal or stores the compressed downmix signal and a spatial information signal in a storage medium. In this case, a spatial information signal, which is extracted in downmixing a multi-channel audio signal, is used in restoring an original multi-channel audio signal from a downmix signal.
Configuration information is non-changeable in general and a header including this information is inserted in an audio signal once. Since configuration information is transmitted by being initially inserted in an audio signal once, an audio signal decoding apparatus has a problem in decoding spatial information due to non-existence of configuration information in case of reproducing the audio signal from a random timing point.
An audio signal encoding apparatus generates a downmix signal and a spatial information signal into bitstreams together or respectively and then transfers them to the audio signal decoding apparatus. So, if unnecessary information and the like are included in the spatial information signal, signal compression and transfer efficiencies are reduced.